Figure 10-5


Click on figure for K+ Channel Animation

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Portions of the KcsA K+ channel responsible for its ion selectivity. The X-ray structure of the residues forming the cavity (bottom) and selectivity filter (top) but with the front and back subunits omitted for clarity. Atoms are colored according to type, with C yellow, N blue, O red, and K+ ions represented by green spheres. The water and protein O atoms that ligand the K+ ions, including those contributed by the front and back subunits, are represented by red spheres. The coordination polyhedra formed by these O atoms are outlined by thin lines. Click on the lower K+ channel figure to see the migration of K+ ions down the channel. Note that K+ ions occupying the selectivity filter are interspersed with water molecules and that the K+ ions maintain a constant spacing while traversing the selectivity filter. [Based on an X-ray structure by Roderick MacKinnon, Rockefeller University. PDBid 1K4C.]